The present invention relates to galvanometers and more particularly to galvanometers adapted for mounting in close adjacent spaced relationship to provide a multi-channel galvanometer assembly particularly well suited for use as a multiple pen motor assembly in multi-channel recording instruments such as electroencephalographs and the like.
A typical galvanometer pen motor used in a strip chart type recorder is shown with reference to FIGS. 1 and 2. In such apparatus, a coil of wire 10 is disposed for rotational movement about an axis 12. A pen 14 is operably attached to the coil 10 in such a manner as to rotate therewith about axis 12. Coil 10 and pen 14 are then biased by spring means (not shown) to remain in a neutral position until deflected therefrom by forces as will be hereinafter described. A strip of recording paper 16 is adapted to be moved under pen 14 in the direction of arrow 18 by appropriate drive means (also not shown). As paper 16 passes under pen 14, the pen (typically connected to a supply of liquid ink) causes a permanent recording line 20 to be marked on paper 16 continually and permanently indicating the position of the pen as the paper passes thereunder. Movement of coil 10 and pen 14 from the neutral position is caused by placing coil 10 in a magnetic field and applying varying electrical energy to coil 10. The electrical energy in coil 10 causes magnetic forces to be generated surrounding coil 10 which act in conjunction with the magnetic flux of the magnet field to deflect coil 10 in one direction or the other from the neutral position as indicated by the arrows 22.
In a typical prior art galvanometer assembly as shown in FIGS. 1 and 2, one or more permanent magnets 24 are employed adjacent coil 10 with opposite poles on either side of coil 10 to create the magnetic flux field. Because of the low coercive force of conventional magnets, a soft iron return path connecting the outside poles of the magnets 24 must be provided such as that labeled 26. Iron pole pieces 28 are also often employed so that the distance from the source of magnetic flux to coil 10 will be minimized. Additionally, an iron core 30 is usually disposed within coil 10 to minimize the amount of air gap across which the magnetic flux must flow. Examples of various configurations of such prior art galvanometers can be seen in the following U.S. Pat. Nos. :
866,387 J. Richard PA1 2,102,409 H. T. Faus PA1 2,355,237 T. J. Pethes, Jr. PA1 2,478,329 H. B. Shaper PA1 2,526,329 H. H. Chamberlain PA1 2,535,065 C. A. Heiland PA1 2,660,510 A. M. Grass PA1 2,688,729 F. F. Offner PA1 3,728,735 J. A. Burton
An electroencephalograph (EEG) employs a plurality of galvanometer pen motors mounted in close adjacent spaced relationship to provide a multi-channel recorder output such as that shown in FIG. 3. Such an arrangement is shown in the patents to Shaper, Heiland, and Grass cited above. The signal being detected from each single electrode attached to the patient's scalp is amplified and conducted to an individual galvanometer pen motor 40 by electrical circuitry (not shown) which forms no part of the present invention. By shifting the position of the magnetic flux gap and turning the position of the pen 14' 90.degree., prior art galvanometer pen motors such as shown in FIGS. 1 and 2 can be disposed in close adjacent spaced relationship to provide the multi-channel recorder output 42 of FIG. 3. The above referenced patent to Shaper illustrates this approach. Because of the space occupied by the individual pen motors 40 in such an arrangement, the supply of paper 16 must be adapted to pass along guide means such as roller 44 shown in FIG. 4 in order to pass under pens 14' in the presence of galvanometer motors 40.
In a portable EEG instrument as presently employed in many medical applications, use of such inherently large galvanometer type recorder pen motors limits the number of channels which can be provided on the recorder as well as making the instrument itself heavy and cumbersome for portable use. Moreover, servicing and/or replacement of an individual channel galvanometer pen motor requires the complete removal and replacement of the total pen motor assembly. If an instrument is sold with less than a full complement of pen motors, the later addition of additional channel recording capability requires the costly purchase and complex installation of a complete galvanometer pen motor for each of the desired additional channels.
Wherefore, it is the object of the present invention to provide a multi-channel galvanometer assembly which is lighter and more compact than that possible employing the technique of the prior art and which is readily expandable and easily serviced.